This invention relates to a seed planter, to a planter assembly and to a method of picking up and discharging single seeds. More specifically, the invention relates to a seed planter, planter assembly and method in which accurate metering of the seeds is achieved by holding the seeds against a surface by means of jets of gas.
In the application, the term "seed planter" is used to denote an apparatus which supplies a single stream of seeds, theoretically one at a time. In normal agricultural use, a machine is used which comprises a number (typically about 20) of seed planters mounted upon a framework and provided with an appropriate drive mechanism to supply power to the planters. Such a machine, which is normally referred to by farmers as a "planter" is designated herein by the term "planter assembly".
A seed planter must be designed having regard to several different, and often antipathetic, requirements. The planter should of course not damage the seed which it handles, since damage to the seed will reduce the germination rate and consequently the crop yield. In most cases, the seeds should be planted one at a time, and the spacing along a row of seeds should conform accurately to a predetermined value; however, since it may be necessary to vary the spacings between rows because of the type or variety of seeds being planted or because of the environmental conditions under which the seed will be grown, the seed planter should be capable of adjusting the row spacing when desired. In order to reduce the time and cost of planting, the planter should be capable of delivering seeds accurately at a predetermined spacing when the tractor towing a planter assembly incorporating the planters is moving across the field at its maximum working speed, which in the case of most modern tractors is about seven miles (11 km.) per hour. The metering rates involved in operating at this speed are considerable; for example, if seeds are being planted with a six inch (15 cm.) spacing between adjacent seeds in each row, when the tractor is moving at seven miles per hour the planter must meter more than 20 seeds per second. Accuracy of timing in delivering the seeds is crucial; for example, in the example previously given where the planter is metering above 20 seeds per second, a delay of only 50 milliseconds in delivering one seed will cause two seeds to issue from the planter simultaneously, so that one planting position will not receive a seed while the next will receive two seeds instead of one. Even when the actual metering part of the seed planter functions correctly, delays on the order of 100 milliseconds are common in commercial planters because such planters frequently incorporate a delivery chute to control the movement of the seeds after they have passed through the metering part of the planter, and the varying angles at which the metered seeds strike the walls of this delivery chute cause variations in the time of delivery of the seeds. Finally, it is important that a planter have a small width, since the minimum spacing between rows which a planter assembly can achieve is governed by the width of the individual planters. (It is possible to mount two separate rows of planters on a planter assembly, planters in the two rows planting alternate rows of seeds so that the minimum spacing between adjacent rows can be half the width of the planter, but such an arrangement increases the size, complexity and weight of the planter assembly, in particular a more complicated drive train arrangement is needed to supply power to the two rows of planters.)
In the case of corn and some other crops, no existing planter adequately fulfills all the above requirements. One early type of planter comprised a cylindrical seed hooper having a vertical axis. A circular recess was formed in the base of the hopper and within this recess rotated a disc having semicircular cutouts at regular intervals around its periphery. When seed was placed in the hopper, seeds became lodged in the cutouts in the wheel, theoretically at the rate of one seed per cutout, and were transported around the recess as the wheel rotated. A shield was fixedly mounted within the hopper so as to extend above a portion of the periphery of the rotating wheel, leaving only a small clearance between the upper surface of the wheel and the shield, so that the only seeds which were permitted to enter beneath the shield were those trapped in the cutouts in the wheel. While passing beneath the shield, the cutouts passed successively over a seed discharge opening formed in the bottom of the hopper and were thus allowed to fall from the cutouts onto the ground, the small clearance between the upper surface of the wheel and the shield preventing seeds not received in the cutouts flowing from within the hopper through the seed discharge opening.
This type of planter achieves reasonably accurate metering of the seed, but is only useable at relatively low metering speeds of about ten seeds per second (equivalent to a tractor speed of about four miles per hour). The friction between the wheel and the seeds lying in contact with its upper surface, and between the seeds lodged in the cutouts and the base of the hopper, causes damage to the seeds, and this seed damage increases sharply with tractor speed. At tractor speeds above about four miles per hour, damage to the seed becomes too severe to be acceptable.
A second commercially-produced type of planter comprises a disc rotating in an inclined plane. Twelve "fingers" are distributed over one face of the disc at regular angles. Each of these fingers comprises a shaft capable of pivoting about its own axis and extending substantially radially of the disc and a flat blade extending at right angles to the shaft and lying adjacent the periphery of the disc. A rather complicated cam mechanism is provided to pivot each of the shafts individually between an open position, in which the blade extends away from the plane of the disc at an angle of about 40.degree. to that plane, and a closed position, in which the blade lies substantially parallel to the disc. Seeds flow from a hopper into the lowest part of a cylindrical chamber, of which the disc forms one end wall, and the fingers descend successively through the mass of seeds at the bottom of the chamber. As each finger reaches the lowest point in the chamber, the cam mechanism pivots the shaft of that finger so as to move the blade from its open to its closed position, thus (in theory) trapping a single seed between the blade and the adjacent surface of the disc. As the disc rotates, the seed thus trapped is then carried upwardly past a brush which serves to return any excess seeds which may be adhering to the blade back to the bottom of the chamber. As the blade passes its highest point, the cam mechanism returns the blade from its closed to its open position, thus releasing the trapped seed and allowing it to fall through a seed discharge opening provided adjacent to this point.
Although this seed planter is capable of operating at higher metering speeds than the first type of seed planter described above, it is not capable of metering accurately over a wide range of metering speeds. At low metering speeds, less than about ten seeds per second, the number of seeds delivered is less than the theoretical quantity of one seed per finger per revolution. At metering speeds of the order of about 25-30 seeds per second, the amount of seeds metered is close to the theoretical amount, while at metering speeds as high as about 40 seeds per second, the amount of seed actually delivered exceeds the theoretical amount, in practice usually by as much as about 50%. Farmers are inclined to operate this planter at considerably higher speeds than those recommended by the manufacturer, thus resulting in considerable overplanting. Not only does this overplanting waste seed, but experiments have shown that overplanting actually reduces crop yields, since if more than one seed is planted in a given spot and two or more seeds germinate in the same spot, all the resultant plants tend to be undersized and relatively unproductive. Furthermore, it will be apparent that, because the amount of seed as a proportion of the theoretical amount varies with the metering speed of this type of seed planter, it is difficult to secure uniform application of seed to a field where working conditions (such as field conditions or gradients) force the operator to vary tractor speed in various parts of the field.
A third commercially-produced type of seed planter comprises a disc-shaped rotor disposed in a vertical plane and carrying around its periphery a series of cups. The cups are arranged so that, on the edge of the rotor which is moving upwardly, the cups are open downwardly. A mass of seeds is disposed in the lowest portion of a seed chamber disposed adjacent one side of the rotor, and seeds are forced by air pressure into the cups. The seeds thus trapped in the cups are carried over the highest point on the rotor and, while the cups are descending, the flow of air is interrupted, thus allowing the trapped seeds to fall from the cups. The chief disadvantage of this type of seed planter is the considerable overplanting which it produces; in practice, if the air flow is made strong enough to ensure that at least one seed is trapped in each cup to provide adequate seed planting, in a large proportion of the cups two, three or even more seeds will be trapped. The resultant overplanting leads to the same problems as described above with reference to the second type of seed planter.
All the above types of seed planter also suffer from the problems of timing in delivering their seeds, already discussed above.
The accurate metering of seeds is rendered even more difficult when the seeds to be metered have a flattened shape; important commercial seeds of this type include seed corn and cucumber seeds. If one attempts to use any conventional planter to plant such seeds overplating will result because, whatever type of receptacle is provided in the planter to hold the seed, if the receptacle is large enough to hold a single seed flat on (i.e. with one of the large faces of the seed disposed adjacent the base of the receptacle), the receptacle will accommodate two, three, or even more seeds edge on.
U.S. Pat. No. 3,843,018 issued Oct. 22, 1974 to one of us (Robert G. Holmes), U.S. Pat. No. 3,954,204 issued May 4, 1976 to Becker and U.S. patent application Ser. No. 428,097 of even date herewith, filed by the said Robert G. Holmes and entitled "Seed Planter, Planter Assembly and Method of Picking Up and Discharging A Single Seed", all disclose seed planters in which individual seeds are retained within depressions in a rotor by means of a jet of gas passing through the depression. Both the planters described in U.S. Pat. No. 3,843,018 and in the aforementioned U.S. patent application Ser. No. 428,097 are capable of accurately metering spherical or near-spherical shaped seeds, but, as explained in the aforementioned patent application, are not suitable for metering flat seeds since flat seeds will not develop the necessary Bernoulli forces needed to trap the seed within the depression.
It will thus be seen that there is a need for a seed planter which can accurately meter flat seeds at high metering rates, and this invention seeks to provide such a planter.